Methods for forming image sensors

Abstract

Methods for forming image sensors that leverage cavity profiles and induced stresses. In some embodiments, the method includes forming a cavity in a substrate where the cavity has a cavity profile that is configured to accept a sensor pixel structure for an image sensor, forming at least one passivation layer in the cavity, and forming at least one optical layer in the cavity on at least a portion of one of the at least one passivation layer. The at least one optical layer is configured to provide, at least, pixel-to-pixel optical isolation of the sensor pixel structure. The method further includes forming the sensor pixel structure in the cavity on the at least one optical layer of the sensor pixel structure where the cavity profile is configured to control stress on the sensor pixel structure.

The invention claimed is: 
     
       1. A method for forming an image sensor, comprising:
 forming a cavity on a substrate, the cavity having a cavity profile and configured to accept a sensor pixel structure of the image sensor; 
 forming at least one passivation layer in the cavity; 
 forming at least one optical layer in the cavity on at least a portion of one of the at least one passivation layer, wherein the at least one optical layer is configured to provide, at least, pixel-to-pixel optical isolation of the sensor pixel structure; and 
 forming the sensor pixel structure in the cavity on the at least one optical layer of the sensor pixel structure, 
 wherein the cavity profile is configured to control stress on the sensor pixel structure. 
 
     
     
       2. The method of  claim 1 , further comprising:
 forming the sensor pixel structure using an atomic layer deposition (ALD) process, a chemical vapor deposition (CVD) process, or a molecular beam epitaxy (MBE) process; and 
 crystallizing the sensor pixel structure. 
 
     
     
       3. The method of  claim 1 , wherein the at least one passivation layer or the at least one optical layer is conformally deposited into the cavity. 
     
     
       4. The method of  claim 1 , wherein the image sensor includes multiple stacked sensor pixel structures within the cavity separated by optical layers. 
     
     
       5. The method of  claim 1 , wherein the at least one optical layer includes a distributed Bragg reflector (DBR) mirror layer or a DBR filter layer. 
     
     
       6. The method of  claim 1 , further comprising:
 depositing a charge passivation layer in the cavity prior to forming the sensor pixel structure, the charge passivation layer configured to increase a quantum efficiency of the image sensor by altering a work function or an electric field of the sensor pixel structure. 
 
     
     
       7. The method of  claim 1 , further comprising:
 adjusting an amount of stress applied to the sensor pixel structure prior to or after formation of the sensor pixel structure in the cavity, wherein adjusting the amount of stress increases a quantum efficiency of the sensor pixel structure. 
 
     
     
       8. The method of  claim 7 , wherein the amount of stress is adjusted by placing at least one isolation structure external of the cavity of a material different from the substrate beside the cavity and wherein the amount of stress is further adjusted by differing material selections of the material different from the substrate for the external isolation structure. 
     
     
       9. The method of  claim 8 , wherein the at least one isolation structure is at least one shallow trench isolation structure or at least one deep trench isolation structure gapfilled with the material different from the substrate. 
     
     
       10. The method of  claim 7 , wherein the amount of stress is adjusted by curing processes, implanting dopants, or annealing processes prior to or after forming the sensor pixel structure. 
     
     
       11. The method of  claim 1 , further comprising:
 etching a bottom of the cavity to reveal substrate material; and 
 forming the sensor pixel structure in the cavity using an epitaxial growth process. 
 
     
     
       12. The method of  claim 1 , further comprising:
 forming a plurality of stacked sensor pixel structures in the cavity separated by optical layers; and 
 forming a plurality of electrical contact vias to each of the plurality of stacked sensor pixel structures only on a single side of the image sensor. 
 
     
     
       13. The method of  claim 1 , wherein the at least one optical layer is formed of a metal material or dielectric material. 
     
     
       14. A method for forming an image sensor, comprising:
 forming a hardmask pattern on a substrate; 
 etching at least one cavity in the substrate based on the hardmask pattern, the at least one cavity having a cavity profile and configured to accept a sensor pixel structure of the image sensor; 
 removing the hardmask pattern from the substrate; 
 forming at least one conformal passivation layer in the at least one cavity; 
 forming at least one conformal optical layer in the at least one cavity on at least a portion of the at least one conformal passivation layer, wherein the at least one conformal optical layer is configured to provide, at least, pixel-to-pixel optical isolation of the sensor pixel structure; and 
 forming the sensor pixel structure in the at least one cavity on the at least one conformal optical layer of the sensor pixel structure. 
 
     
     
       15. The method of  claim 14 , further comprising:
 forming the sensor pixel structure using an atomic layer deposition (ALD) process or a chemical vapor deposition (CVD) process; and 
 crystallizing the sensor pixel structure. 
 
     
     
       16. The method of  claim 14 , further comprising:
 adjusting an amount of stress applied to the sensor pixel structure by altering the cavity profile, wherein adjusting the amount of stress increases a quantum efficiency of the sensor pixel structure. 
 
     
     
       17. The method of  claim 14 , further comprising:
 forming a charge passivation layer prior to forming the sensor pixel structure, wherein the charge passivation layer is configured to increase a quantum efficiency of the sensor pixel structure. 
 
     
     
       18. A non-transitory, computer readable medium having instructions stored thereon that, when executed, cause a method for forming an image sensor to be performed, the method comprising:
 forming a cavity into a substrate, the cavity having a cavity profile and configured to accept a sensor pixel structure of the image sensor; 
 forming at least one passivation layer in the cavity; 
 forming at least one optical layer in the cavity on the at least one passivation layer, wherein the at least one optical layer is configured to provide, at least, pixel-to-pixel optical isolation of the sensor pixel structure; and 
 forming the sensor pixel structure in the cavity on the at least one optical layer of the sensor pixel structure. 
 
     
     
       19. The non-transitory, computer readable medium of  claim 18 , wherein the cavity profile is configured to control stress on the sensor pixel structure to increase quantum efficiency. 
     
     
       20. The non-transitory, computer readable medium of  claim 18 , wherein one of the at least one optical layer is a distributed Bragg reflector (DBR) configured to provide optical isolation for the sensor pixel structure.